1. Field of the Invention
The present invention relates to an improved optical information recording medium for use in the field of optical information recording.
2. Description of Background
Up until the present time, a recording layer comprising a metal with a low melting point or a metal with a low melting point and a dielectric material on a substrate have been provided as an optical information recording medium, but these information recording media have such drawbacks as poor storage characteristics, low resolution, low recording density, difficult production conditions, and high cost. Accordingly, recording layers in which an organic dye layer is substituted for the metallic layer have recently been proposed. Because this organic dye layer has the advantages of a low melting point and a low decomposition temperature, as well as a low coefficient of thermal conductivity, a recording layer with high sensitivity and high density is possible, and, in addition, because it is possible to use a coating method to form the layer, high productivity and low cost can be expected. Conventionally, the use of layers of a cyanine dye and a merocyanine dye as the organic dye layer is commonly known. However, in a recording layer fabricated from this type of dye, the absorption maximum wavelength and the reflection maximum wavelength differ. Therefore, the drawback exists that it is not possible to obtain both high sensitivity recording and high contrast reproduction using a simple pick-up.
In order to solve this problem, a recording material from a mixture of a dye with an absorption maximum close to the wavelength of the recording and reproduction beam and a dye with a reflection maximum also close to this wavelength has been proposed in Japanese Laid-Open Patent Applications 1-113288 and 1-178493, to provide both high sensitivity recording and high contrast reproduction.
In addition, from another viewpoint, the provision of a protective layer with a refractive index larger than that of a recording layer has been proposed for application to the recording layer to provide a high reflection coefficient and therefore high contrast reproduction in an optical information recording medium using an organic dye. However, the following problems remain to be solved in the above-mentioned conventional technology. Specifically, because a recording layer comprising a mixture of a dye exhibiting an absorption maximum close to the wavelength of the recording and reproduction beam and a dye with a reflection maximum also close to this wavelength is a mixed system, this results in poor compatibility of the two dyes, leading to the problem that crystallization or defects are produced during storage. This is one possible cause of error generation. In addition, the reflectivity of the recording layer is still not adequate, so a material with a higher reflectivity is required. Also, in the case where a protective layer with a refractive index larger than that of a recording layer is provided, a high reflectivity can be obtained by making the recording layer thin. However, because the protective layer itself has no absorption, the sensitivity is still not sufficiently high.